To cast doubt on CD's view that volcanic action is associated with elevation of land, CL suggests that local oscillations in strata underlying volcanoes could also explain how active volcanoes have uplifted fossil deposits of marine shells. Overall he is more inclined to believe that recent volcanoes belong to areas of subsidence rather than of elevation.

Transcription

Of course it is true, as you well show in your Coral volume, that the active volcanos
have recent deposits with marine shells uplifted in them.
This is the case to some small extent in all the principal Atlantic islands except
Palma, which I visited, & Palma has not been thoroughly examined & may
somewhere exhibit signs of elevation Comparatively therefore, and by contrast with the
Atoll areas, you may represent the volcanic as rising.

Still I have always felt a little uncomfortable at being called upon to assume that in
recent & pliocene ages volcanic action has been and is connected with the growth
of land. Were this the case should we not find that the continents would be the great
areas of extinct Pliocene and of active volcanos, and that the latter did not affect
sea-side and insular and even mid-ocean sites.

If we find active volcanos in Oceanic areas, & few or none of them in the
middle of continental areas, it furnishes a primâ facie case in favour of the
doctrine that the grand uplifting power acts very independently of the accidental sites
of existing superficial outbreaks. An argument might even be raised in support of the
theory that active volcanos are more connected with sinking on a great scale however
true it may be that locally they tend to upheave as well as to form land by outpouring
of lava & of ejectamenta.

Maurys last chart of the Atlantic makes the Atlantis
hypothesis more bold than it appeared when E. Forbes proposed it for the
Canaries are separated from Africa & Europe by deep sea depressions of more than
6000 feet & Madeira by depths exceeding 12,000 feet! The data, I fear are scanty however.

I find in Madeira & the Canaries upraised littoral deposits of the Miocene
period, in my sense of Miocene when there was a certain proportion of living species
already in being. This, I think, rather increases the difficulty of the continental
extension hypothesis.

But I want to ask you whether it may not be true that the bed of the Atlantic has been
gradually sinking all the while the Canaries & Madeiras have been forming
& that very slight local upheaval only has occurred even on the sites of these
volcanic islands. I sometimes think I can dispense with all excess even of local
upheaval, over & above that of the adjoining deep sea spaces.

Thus for example suppose A. B. C. to represent the original Europeo-African
continent & B. D. to be the level of the Atlantic. A gradual sinking down of 6000 feet takes place in a short part of the
Miocene Period, (not occupying possibly above 12 a million of years.

The ocean has thus risen relatively to the land up to G. But in the meantime
the volcano F. has been gradually built up 7500 ft
& is 1500 feet higher above the sea. A pause in the volcanic action
takes place during which a subsidence of partial extent under
Id occurs causing F. to lose
1500 feet of its height by slow depression during which every part of the
subaerial mass of F. gets submerged & covered or faced with a marine
littoral deposit, full of rolled boulders and pebbles with [DIAGRAM HERE] q H
p patellæ, & other littoral shells. The subjacent rocks
H. all volcanic but as entirely free from marine remains as if exclusively
subaerial.

We now have the original subterranean layer K. L. bending down at m, n, o.
1500 feet below the general depression of 6000 feet, & if it
be then restored to the level m' o' we have the volcano H. pushed up again
1500 feet with the marine beds p. q., abutting against the foundation of older
subaerial rocks. This is what I observed in one part of the
Grand Canary.

The 4000 or 5000 of additional subaerial volcanic beds may be built
up & you have Madeira. In the Grand Canary I suspect most of its height was
attained before the submergence of 1500 or (1100? feet. [DIAGRAM HERE]
marine beds older subaerial Grand Canary

But my reasoning you see is the same as that which I adopted about the Atolls before
you invented your theory, namely, that oscillations occurring in a sea filling up with
coral or with volcanic matter may cause uplifted marine formations provided subsidence
& upheaval be just equal the one to the other.

Take away all the volcanic matter from Etna, Ischia &c & the marine
shells could sink down below the sea level. All the marine beds in the Canaries
& Madeiras are volcanic except the corals & shells themselves. If the
active volcanos were connected with a continent-making power, we should see secondary
and non-volcanic rocks uplifted by them.

I do not however want to contend that active & Pliocene volcanos belong to
subsiding areas rather than to areas of elevation altho' half inclined to that
alternative in preference to the opposite theory. But surely they are so distributed as
that they seem to belong quite as much to Pliocene & recent subsidence as to
upheaval during the same period.

The letter has not been found. The heading, date, and text given here are taken from
Lyell's scientific journal 2, pp. 82–90 (Kinnordy House MS).
It is also printed in Wilson ed. 1970, pp. 110–14.

+

f2 1915a.f2

Coral reefs (1842), pp. 140–2, ‘On the absence
of active Volcanos in the areas of subsidence, and on their frequent presence in the
areas of elevation’. Lyell had queried CD's suggestion that volcanoes
were mostly associated with rising land in his scientific journal 2, p. 74, in
an entry dated 30 June 1856 (Wilson ed. 1970, p. 108):
There has always seemed to me a difficulty in reconciling two facts in
Darwin's theory of volcanic & Coral areas—namely that
Volcanoes are the upheaving power and yet, that nearly all the islands in the middle
of great oceans are volcanic, whereas there are not many active, nor an extraordinary
number of Tertiary volcanoes in continental areas.

+

f3 1915a.f3

Maury 1855a, which Lyell had been studying with reference to the possibility of
former land-bridges between Madeira and Africa (see Wilson ed. 1970,
pp. 109–10).

Lyell refers to the first diagram given at the beginning of his extract, dated
‘June 1st’, in his
scientific journal (Wilson ed. 1970, p. 111).

+

f6 1915a.f6

Lyell refers to the second diagram given at the beginning of his extract.

+

f7 1915a.f7

C. Lyell 1830–3, 2: 283–301.

+

f8 1915a.f8

Following the letter, Lyell added: P.S. not sent to Darwin The
deepness of the sea round Madeira &
Po
So & other Atlantic Islands is
against Volcanos being connected with upheaval for the upraising power
wd tend at least to render the sea shallow
shd it fail to push up dry land in the
neighbourhood of oceanic volcanos. July
2d—/56